A variety of approaches have been developed in recent years to recruit CD8+ T cells for the control of cancer due to their recognized potency to destroy tumor cells. One of the most promising approaches to date is the use of adoptive T cell transfer, with particular success in metastatic melanoma patients. Recent progress has been made toward defining the mechanisms that promote effective adoptive T cell-based immunotherapy of cancer. However, the variables that determine success versus failure, particularly for cancers beyond melanoma, remain poorly defined. The broad objective of this proposal is to identify mechanisms that promote CD8+ T cell-mediated elimination of established autochthonous tumors using adoptive T cell-based immunotherapies. The hypothesis driving this study is that the effectiveness of T cell- based adoptive immunotherapy of cancer will vary with the distinct histological origin of the tumor and the CD8+ T cell epitope targeted due to differential effects on the tumor microenvironment. The following specific aims will be pursued. Specific Aim 1. Define the mechanisms that promote regression of established autochthonous brain tumors following radiation-enhanced adoptive immunotherapy. Specific Aim 2. Evaluate the sensitivity of tumors from unique tissue origins to adoptive T cell immunotherapy. Specific Aim 3. Identify mechanisms critical for adoptive T cell immunotherapy targeting a weak tumor-associated determinant. In this study, mice that express the SV40 large T antigen oncoprotein from tissue-specific promoters will be used to investigate mechanisms that regulate effective adoptive T cell immunotherapy toward tumors that arise in distinct tissues. This will include models of brain, pancreas and prostate cancer. The SV40 T antigen system provides a powerful model to address these issues due to the availability of multiple well-established transgenic mouse tumor models and the large array of reagents available to monitor T antigen-specific CD8+ T cell responses to multiple determinants derived from the same protein antigen. Localized versus systemic effects of radiation associated with successful T cell-mediated tumor regression will be defined in order to more specifically design immunotherapies for established tumors. In addition, the efficacy of radiation-enhanced adoptive T cell transfer to control tumors of unique histological origin will be assessed by defining changes in the T cell phenotype and tumor microenvironments that are associated with successful immunotherapy. Finally, we will identify approaches that overcome the limitations of targeting a weak tumor-associated determinant by adoptive immunotherapy in order to broaden the repertoire of available targets. By testing these approaches in a tumor system where the antigen and the effectors' T cell population are held constant, the results of these studies should reveal tumor-specific mechanisms that promote and/or inhibit successful adoptive T cell-based immunotherapy. This new knowledge should provide insight for increasing the success of translational adoptive T cell-based immunotherapy approaches against diverse cancers.